Liquid cooling of high current devices in power flow control systems

ABSTRACT

A modular liquid cooling block is described for cooling high current devices deployed in power flow control systems. The liquid cooling blocks may have separate shower heads which may be configured for direct impingement, indirect impingement, or parallel flow cooling configurations. Voltage isolation of liquid cooling blocks from an enclosure of the power flow control system and from associated equipment enables serial or parallel connected power flow control units to inject substantial reactive power that may be configurable into a power transmission line. Associated power flow control systems are monitored for temperature, flow rate and pressure gradient. Redundant pumps and fan radiators contribute to reliable operation. Automatic shutdown and alarm may be provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.16/948,523 filed on Sep. 22, 2020, which claims the benefit of U.S.Provisional Application No. 62/987,221 filed on Mar. 9, 2020, thedisclosures of which are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The subject technology of this disclosure relates generally to powerflow control systems. More particularly, the subject technology relatesto a liquid cooling block and to cooling of a power flow control unitusing a liquid cooling block.

BACKGROUND

Modern-day distributed power generation and distribution systems haveintroduced multi-generator grids and new modes of operation. These newmodes of operation may introduce power electronic (PE) converters, suchas power flow control systems used to inject reactive impedance orreactive power into transmission lines. These systems may include highcurrent devices that generate high thermal loads. To date, power flowcontrol systems have typically used air cooling for heat dissipation.There is a need in the art for liquid cooling configurations adapted foruse in power flow control systems.

SUMMARY

A first aspect of the subject technology relates to a liquid coolingblock (LCB). The LCB includes input and output ports and aclosed-circuit fluid assembly coupled to the ports. A pump is used tocirculate liquid coolant within the LCB and within the closed-circuitfluid assembly, and a showerhead is provided with an array of jettingapertures. A cooling plate is provided, and an electronic assembly isthermally coupled to the cooling plate. Jets of liquid coolant createdby the jetting apertures may impinge directly onto the cooling plate oronto a metal member thermally coupled to the cooling plate.

A second aspect of the subject technology relates to a power flowcontrol unit. The power flow control unit includes a bank of capacitorsconnected in parallel to form a DC capacitor, a LCB within which liquidcoolant circulates, and a high power switching assembly thermallycoupled to the LCB and electrically coupled to the DC capacitor.

A third aspect of the subject technology relates to a power flow controlsystem including an enclosure and several power flow control unitscontained within the enclosure. Each power flow control unit may includea bank of capacitors connected in parallel to form a DC capacitor, a LCBwithin which liquid coolant circulates, and a power switching assemblythermally coupled to the LCB and electrically coupled to the DCcapacitor. The power flow control system may be configured to injectreactive power of at least 10 MVAr (mega-volt-amp reactive) into a powertransmission line.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are provided together with the followingdescription of various aspects and embodiments of the subject technologyfor a better comprehension of the invention. The drawings and theembodiments are illustrative of the invention and are not intended tolimit the scope of the invention. It is understood that a person ofordinary skill in the art may modify the drawings to generate drawingsof other embodiments that would still fall within the scope of theinvention.

FIG. 1 is a perspective drawing of a liquid cooling block in anembodiment of the present disclosure.

FIG. 2 is a cross-sectional view of a liquid cooling block, showingcoolant circulation paths according to one embodiment.

FIG. 3 depicts optional surface configurations for cooling plates usedin liquid cooling blocks according to some embodiments.

FIG. 4 is a schematic of a thermal architecture used for cooling aninverter module of a power flow control unit according to oneembodiment.

FIG. 5 is a perspective drawing of a power flow control unit configuredto inject 1 MVAr into a power transmission line according to oneembodiment.

FIG. 6 shows the series and parallel connection of isolated power flowcontrol units, together with a bypass circuit according to oneembodiment.

FIG. 7 illustrates an enclosed power flow control system configured toinject 10 MVAr into a power transmission line according to oneembodiment.

DETAILED DESCRIPTION

Examples of various aspects and variations of the subject technology aredescribed herein and illustrated in the accompanying drawings. Objects,features, and advantages of the invention will be apparent from thefollowing detailed description taken in conjunction with theaccompanying drawings. While various embodiments of the subjecttechnology are described, the following description is not intended tolimit the invention to these embodiments, but rather to enable a personskilled in the art to make and use this invention.

A modular liquid cooling block (LCB) is described for cooling highcurrent devices deployed in power flow control systems. The LCB may haveseparate shower heads which may be configured for direct impingement,indirect impingement, or parallel flow cooling configurations. Voltageisolation of liquid cooling blocks with associated equipment enablesseries or parallel connected power flow control units to injectsubstantial reactive power that may be configurable into a powertransmission line. Associated power flow control systems that includethe serial or parallel connected power flow control units are monitoredfor temperature, flow rate and pressure gradient. Redundant pumps andfan radiators contribute to reliable operation. Automatic shutdown andalarm are provided.

A first aspect of the present disclosure relates to a LCB that includesinput and output ports and a closed-circuit fluid assembly coupled tothe ports. A pump is used to circulate liquid coolant within the LCB anda showerhead is provided with an array of jetting apertures. A coolingplate is provided, and an electronic assembly is thermally coupled tothe cooling plate. Jets of liquid coolant created by the jettingapertures impinge directly onto the cooling plate or onto a metal memberthermally coupled to the cooling plate. The cooling plate may bepatterned with three-dimensional features to improve coolingperformance, and the cooling plates may be interchangeable to providevariations in the cooling plate. The LCB may have a clamshellconstruction wherein two halves of a fluid chamber are welded together.Other joining methods such as friction stir welding may be used. Theelectronic assembly thermally coupled to the cooling plate may comprisehigh-current devices, and the high-current devices may be insulated gatebipolar transistors (IGBTs). In one embodiment, the showerhead maycomprise a slot through which liquid coolant is injected, rather than anarray of jetting apertures. The LCB may be thermally coupled to a fanradiator for radiating heat to an air ambient. The liquid coolant maycomprise mixtures of water, ethylene glycol, and poly-ethylene glycol.The water may be distilled water or de-ionized water.

A second aspect of the present disclosure relates to a power flowcontrol unit which includes a bank of capacitors connected in parallelto form a DC capacitor, a LCB within which liquid coolant circulates,and a high power switching assembly thermally coupled to the LCB andelectrically coupled to the DC capacitor. The power flow control unitmay be configured to inject 1 MVA (mega-volt-amp) of reactive power (or1 MVAr) into a power transmission line. It may employ replaceablecomponents and have an operational lifetime of at least ten years. Therequired volume of liquid coolant may be less than 10 liters. The liquidcoolant may be drainable and replaceable and have an operating pressureof less than 4 bars. The LCB may be configured to operate in a range ofambient temperature from −40° C. to 50° C.

A third aspect of the present disclosure relates to a power flow controlsystem comprising an enclosure and several power flow control unitscontained within the enclosure. Each power flow control unit may includea bank of capacitors connected in parallel to form a DC capacitor, a LCBwithin which liquid coolant circulates, and a power switching assemblythermally coupled to the LCB and electrically coupled to the DCcapacitor. The power flow control system may be configured to injectreactive power of at least 10 MVAr into a power transmission line. Thepower flow control system may further include a bypass circuit connectedin parallel, and configured to carry a fault current in excess of thenormal operating current of the power flow control system. Each powerflow control unit may be voltage isolated from other power flow controlunits in the power flow control system.

FIG. 1 illustrates a LCB 10 in an embodiment of the present disclosure.LCB 10 has a clam shell construction, where two halves may be joinedtogether to form interface 11. Each half of the LCB is machineaccessible for machining the shaped internal cavities. A water inletport 12 and a water outlet port 13 are shown. Two sets of four threadedmounting holes, 14 a, 14 b, 14 c and 14 d are provided on each side ofLCB 10 for mounting electronic modules to be cooled. An alternativemanufacturing method is to fabricate a LCB using polymer material andjudiciously place metal frames to which cooling plates may be attachedto provide thermal interfaces to the electronic modules.

FIG. 2 illustrates in cross-section the flow of liquid coolant inside anLCB according to one embodiment. Coolant entering at inlet port 12 isrouted to an array of showerheads 21. Each showerhead includes an arrayof jetting apertures 22, such as nine jetting apertures per showerheadshown in the figure. After jets of coolant have impinged on a coolingplate, or on a metal wall coupled to a cooling plate, the coolant isrouted to outlet port 13. Arrows 23 depict the directional flow of theliquid coolant. Other embodiments of the LCB 10 may include differenttypes of nozzles, active flow control circuits, or other types ofchannel assemblies to increase the flow rate of the liquid coolant nearcritical thermal junctions, or to increase the surface area contacted bythe liquid coolant.

Liquid cooling blocks of the present disclosure may be configured toprovide individualized flow channels using direct impingement, indirectimpingement, parallel flow, or combinations thereof. For directimpingement the jets of coolant fluid impinge directly on a coolingplate. For indirect impingement the jets of coolant fluid impinge on ametal wall of a fluid chamber which is thermally coupled to a coolingplate. For parallel flow the coolant fluid exits from a slot rather thana jetting aperture and passes over a cooling plate or a metal wallthermally coupled to a cooling plate with parallel flow. In each ofthese three cases the cooling plate is thermally coupled to anelectronic module with a low thermal resistance between them.

FIG. 3 shows surface configurations for cooling plates (which may beoptional in some embodiments) together with location 31 of a coolantplate integrated with LCB 10 according to some embodiments. The surfacefeatures shown in the examples face the inside of LCB 10, forinteraction with the coolant via jet impingement or parallel flow asdescribed. A planar face of each coolant plate faces outward as shown,for interfacing (e.g., thermally coupled) with an electronic module thatcomprises a matching planar face. An unpatterned or flat cooling plateis shown 32, together with a cooling plate 33 having vertically orientedfeatures or patterns 33 b (e.g., semi-cylinder patterns) embossedthereon, plate 34 having horizontally oriented features or patterns 34 b(e.g., semi-cylinder patterns) embossed thereon, cooling plate 35 havingfeatures or patterns 35 b (e.g., an array of square or cube shapedpatterns) embossed thereon, and cooling plate 36 having features orpatterns 36 b (e.g., an array of trapezoidal patterns) embossed thereon.Embodiments of the cooling plates may have embossed features of othergeometrical shapes. The embossed features 33 b, 34 b, 35 b, 36 bincrease the surface area on which the coolant jets impinge or otherwiseflow, thereby leading to improved heat transfer.

FIG. 4 illustrates a thermal subsystem 40 of the present disclosure forcooling an electronic module 41 according to one embodiment. Electronicmodule 41 generates heat 42 that is transferred to LCB 10. LCB 10 iscoupled to a radiator 43 through a hot coolant link 44 and a coldcoolant link 45. A fan 46 directs air 46 b onto radiator 43, andradiator 43 transfers heat 43 b to the ambient environment 47. Theliquid coolant may be water or a mixture of water and ethylene glycol orpolyethylene glycol for example. The plumbing of thermal subsystem 40may comprise brazed assemblies that can withstand an operating pressureof 2-5 bar for example. In one embodiment, the liquid coolant may bedrainable and replaceable and have an operating pressure of less than 4bars. Such brazed assemblies may be pressure tested and may have alifetime greater than 10 years. The total volume of liquid coolant inthermal subsystem 40 may be 4-10 liters for example and the flow ratemay be 10-20 liters per minute to support a power flow control unit 50as will be described in reference to FIG. 5 . In some embodiments,sensors of thermal subsystem 40 may monitor the pressure gradient, flowrate, and temperature of the liquid coolant to adaptively control theflow rate or temperature of the liquid coolant via fan 46 or pumps.

Temperature sensors such as negative temperature coefficient thermistors(NTCs) may be used to sense the temperature of the liquid coolant andmay be coupled to an alarm system, to be activated if the coolanttemperature exceeds a predetermined threshold. Thermal subsystem 40 maybe configured with redundant pumps for improved long-termmaintainability and reliability. Tubing used to circulate the coolantmay be made of flexible materials, such as silicone. Thermal subsystem40 comprises a closed-circuit fluid assembly. The thermal architectureof thermal subsystem 40 may be applied to any closed loop coolant systemcoupled to any electronic module 41. In a power flow control system ofthe present disclosure electronic module 41 is configured as an invertermodule containing high-power switching devices and DC capacitors forinjecting reactive power onto a power transmission line.

FIG. 5 illustrates a compact power flow control unit 50 in an embodimentof the present disclosure that includes liquid cooling. The power flowcontrol unit 50 may include at least one electronic module 41 and atleast one LCB 10 of FIG. 4 . A capacitor 51 is shown, one of a bank ofcapacitors that comprise a DC capacitor of the power flow control unit50. AC bus bars 52 a, 52 b are configured to connect to a powertransmission line. A DC bus bar 53 is shown coupled to the DC capacitor.Embedded within power flow control unit 50 may be a pair of liquidcooling blocks, each of which may be LCB 10 as described. A hoist ring54 is also shown. Power flow control unit 50 may be configured to injectreactive power of 1 MVAr into a power transmission line for example.

FIG. 6 illustrates a power flow control system 60 that includes tenpower flow control units 50 described in reference to FIG. 5 accordingto one embodiment. System 60 may include more or less than ten powerflow control units 50 in some embodiments. Power flow control system 60may be configured to provide 10 MVAr of reactive power for injectioninto a power transmission line, for example. Each power flow controlunit 50 may be configured to inject 1 MVAr of reactive power.Connections 61 a and 61 b to the power transmission line are shown. Theten power flow control units 50 are arranged with two parallel unitscomprising a dual unit, and five dual units connected in series. Asshown, voltage isolation of 0.8 kV 62 is provided between each dual unitand an enclosure of power flow control system 60; this may enable seriesconnection of the dual units as shown to provide the desired levels ofinjection of reactive power into a power transmission line connectedbetween nodes 61 a and 61 b. At node 63 the level of voltage isolationis 4.0 kV 64 as shown between the last of the five serially-connecteddual units and the enclosure.

Isolated assemblies 65 a and 65 b are shown. Isolated assembly 65 a maybe power flow control unit 50 described in reference to FIG. 5 .Isolated assembly 65 a includes a power switching assembly 66 thattypically comprises a bank of four insulated gate bipolar transistors(IGBTs) as shown for injecting reactive power from the DC capacitor 51(a bank of parallel-connected DC capacitors of the power flow controlunit 50 in reference to FIG. 5 ) onto the power transmission line. Eachof the IGBTs depicted may comprise two or more IGBT chips connected in abridge configuration. Isolated assembly 65 b comprises a subset of thethermal cooling equipment described in reference to FIG. 4 including aradiator 43, a fan 46 and a pump 67. LCBs 10 are embedded within thepower flow control units 50 as described in reference to FIG. 5 .

Isolated assemblies 65 a and 65 b may comprise structural membersfabricated using non-electrically conductive materials such as fiberreinforced plastic (FRP). One version of FRP comprises a polyester resinand has an operating temperature up to around 140° F. Another version ofFRP comprises an epoxy resin and has an operating temperature up toaround 240° F. Although not required for voltage isolation, tubing forcirculating the coolant may comprise a non-electrically conductivematerial such as silicone. A rail system may be used for mounting thevarious modules of power flow control system 60, enabling convenientaccess for maintenance and replacement, as necessary. Bypass circuitsmay also be included, such as a vacuum switched link (VSL) 68 forproviding an alternate path for bypassing a fault current or for placingpower flow control system 60 into monitor mode, in order to performmaintenance for example. Current limiting chokes 70 a and 70 b may beprovided as shown. A bank 69 of SCRs (silicon-controlled rectifiers) 69a may be provided in parallel as shown, used for bypassing high currentsduring fault conditions on the associated power transmission line. EachSCR 69 a must be capable of withstanding the isolation voltage 64, whichmay be as high as 4.0 kV as shown.

FIG. 7 depicts power flow control system 60 configured as an enclosedsystem 70 according to one embodiment. System 70 includes an enclosure71 having doors 72 for accessing the equipment modules. The modules maybe mounted on rails for convenient access. Nodes 73 a, 73 b areproviding for connection to a power transmission line. Nodes 74 athrough 74 f are provided for connecting the voltage-isolated dual powerflow control units depicted in FIG. 6 .

Embodiments of the disclosure described herein may be applied tostand-alone liquid cooled electronic modules, or to liquid cooled powerflow control units and systems. The devices, processing, and logicdescribed above may be implemented in many different ways and in manydifferent combinations of hardware and software. For example, electroniccircuitry or a controller may be configured with hardware and/orfirmware to execute the various functions described. All or parts of theimplementations may be circuitry that includes an instruction processor,such as a Central Processing Unit (CPU), microcontroller, or amicroprocessor; an Application Specific Integrated Circuit (ASIC),Programmable Logic Device (PLD), or Field Programmable Gate Array(FPGA); or circuitry that includes discrete logic or other circuitcomponents, including analog circuit components, digital circuitcomponents or both; or any combination thereof. The circuitry mayinclude discrete interconnected hardware components and/or may becombined on a single integrated circuit die, distributed among multipleintegrated circuit dies, or implemented in a Multiple Chip Module (MCM)of multiple integrated circuit dies in a common package, as examples.The implementations may be distributed as circuitry among multiplesystem components, such as among multiple processors and memories,optionally including multiple distributed processing systems.

The circuitry may further include or access instructions for executionby the circuitry. The instructions may be stored in a tangible storagemedium that is other than a transitory signal, such as a flash memory, aRandom Access Memory (RAM), a Read Only Memory (ROM), an ErasableProgrammable Read Only Memory (EPROM); or on a magnetic or optical disc,such as a Compact Disc Read Only Memory (CDROM), Hard Disk Drive (HDD),or other magnetic or optical disk; or in or on another machine-readablemedium.

The foregoing description, for purposes of explanation, uses specificnomenclature to provide a thorough understanding of the invention.However, it will be apparent to one skilled in the art that specificdetails are not required in order to practice the invention. Thus, theforegoing descriptions of specific embodiments of the invention arepresented for purposes of illustration and description. They are notintended to be exhaustive or to limit the invention to the precise formsdisclosed; obviously, many modifications and variations are possible inview of the above teachings. The embodiments were chosen and describedin order to best explain the principles of the invention and itspractical applications. They thereby enable others skilled in the art tobest utilize the invention and various embodiments with variousmodifications as are suited to the particular use contemplated. Forexample, while the LCB has been illustrated in conjunction with aninverter of a power flow control unit used to inject reactive power froma DC capacitor into a power transmission line, the principles describedare equally applicable to liquid cooling of other types of powerelectronic converters. The examples are thus illustrative andnon-limiting. It is intended that the following claims and theirequivalents define the scope of the invention.

What is claimed is:
 1. An apparatus of a power flow control unitcomprising: a plurality of capacitors connected in parallel to form a DCcapacitor; at least one liquid cooling block configured to recirculate aliquid coolant; and at least one high-power switching assembly thermallycoupled to the at least one liquid cooling block and electricallyconnected to the DC capacitor, wherein the power flow control unit isconfigured to inject at least 1 MVA (mega-volt-amp) of reactive powerinto a power transmission line.
 2. The apparatus of claim 1, wherein thepower flow control unit is configured of replaceable components thathave an operational lifetime of at least years.
 3. The apparatus ofclaim 1, wherein a volume of the liquid coolant is less than 10 liters.4. The apparatus of claim 1, wherein the power flow control unit isconfigured to operate in a range of ambient temperature from −40° C. to50° C.
 5. The apparatus of claim 1, wherein a pressure of the liquidcoolant does not exceed 4 bar.
 6. The apparatus of claim 1, wherein theliquid coolant is replaceable.
 7. A power flow control systemcomprising: an enclosure; a plurality of power flow control unitscontained within the enclosure, each power flow control unit comprising:a plurality of capacitors connected in parallel to form a DC capacitor;at least one liquid cooling block configured to recirculate a liquidcoolant; and at least one high-power switching assembly thermallycoupled to the at least one liquid cooling block and electricallyconnected to the DC capacitor; wherein the power flow control units areconfigured to inject reactive power of at least 10 MVA (mega-volt-amp)into a power transmission line.
 8. The power flow control system ofclaim 7, further comprising a bypass circuit connected in parallel,wherein bypass circuit is configured to carry a fault current in excessof a normal operating current of the power flow control system.
 9. Thepower flow control system of claim 7, wherein each of the plurality ofpower flow control units is voltage isolated from the enclosure.